When to test for pregnancy

Not all pregnancy tests are the same; some are more sensitive than others…

The most common sign for women to get tested for pregnancy is when they miss their period. Even so, if you are hopeful (or worried) that you are pregnant you can test earlier. You just have to consider that there are many factors to take into account when deciding when to take a pregnancy test. All the information that you need to take into account at this time is described below so just keep reading.

Pregnancy testing

Not all pregnancy tests are the same; some are more sensitive than others. This means that the more sensitive the test is, the earlier it will be able to detect that you are pregnant. Home pregnancy tests detect the presence of human chorionic gonadotrophin or hCG in your urine. These tests are usually qualitative giving a positive or negative result, while blood tests are usually quantitative and give the amount of hCG actually present in the blood. Blood tests are more sensitive and can give a reliable positive result six to eight days after ovulation. The most sensitive home pregnancy tests available are able to confirm pregnancy 7 to 10 days before the start of the period which is equivalent to seven days of conception.

The hCG is made by cells of the placenta and starts to be produced from the moment of the implantation of the egg in the uterine wall. Therefore hCG can only be detected by the most sensitive tests shortly after implantation occurs. This process varies in time, and can occur from 6 to 12 days after ovulation. The variation in implantation date is usually dependent of the ovulation date, and ovulation can be difficult to predict in women with irregular cycles unless there is daily tracking of basal temperature or use of ovulation predictor kits. This means that you cannot take into account the intercourse date to accurately determine when the implantation occurred.

Since sperm can live in the uterus for 5 days and after fertilization the egg can take up to 12 days to attach to the uterine wall, you cannot consider that implantation occurred in the date of the intercourse. Typically, the levels of hCG rise, after implantation of the egg, doubling each 48 to 72 hours, and reach their peak in the first 8 to 11 weeks of pregnancy, after which they decline. The usual threshold to consider a positive result in a pregnancy test is 25mIU/mL and most home pregnancy tests have a detection minimum of 10mIU/mL to 40 mIU/mL.

Therefore, if you take the test too early after conception the levels of hCG will not be high enough, resulting in a false negative. You should choose the most sensitive test available and test only at the time your period would normally occur. Even then, about 10% of women have low hCG, or ovulate later than expected, leading to a false negative result. If you get a negative result, but your period keeps missing and you have other pregnancy signs, you should retake the test after a few days when the hCG levels will be higher and more accurately detected . Keep in mind that pregnancy tests are not 100% reliable and they can give false positives. This can happen for a variety of reasons such as, fertility treatment medications that contain hCG, some kinds of cancer or an early miscarriage.

Levels of hCG

A low-level of hCG can indicate a number of problems such as, a miscarriage, blighted ovum (the fertilized egg is implanted but the embryo does not develop) or an ectopic pregnancy. As with most features of pregnancy the level of hCG varies a lot from woman to woman and hCG levels can be lower than usual without any impact to the development of the pregnancy. Furthermore, the levels of hCG cannot be used as to determine the date of conception. On the other hand, if the hCG is higher than normal it can also indicate problems such as, a molar pregnancy (growth of abnormal tissue within the uterus) or the presence of twins.

In either case, one measurement of hCG in blood is not sufficient for diagnosis, and has to be repeated after 48 to 72 hours. After confirmation of measurements, possible pregnancy problems should be assessed by transvaginal ultrasound. The transvaginal ultrasound is able to confirm more accurately the presence and the state of the pregnancy at 5 to 6 weeks of gestation. This exam can detect a gestational sac and confirm the location of the pregnancy which is useful if there is a suspicion of ectopic pregnancy or miscarriage.

The decision of when to take a pregnancy test is not straightforward since many factors have to be considered. However, remember that if you wait a few days after your missed period you have a low chance of getting a false period. Therefore, it is always better to be patient and let things take their course before taking a test than taking it too soon and keep wondering if it was a false negative. Also, no one knows your body better than you so if you notice something unusual or any symptom of pregnancy do a test just to be sure or consult your doctor to do a blood test that is always more accurate and reliable in determining pregnancy.